Dovetail joints between perpendicular wooden members are well known. Forming a dovetail joint requires cutting a dovetail board and a pin board. As shown in FIG. 1a, dovetail board 11 includes dovetail sockets 70 separating dovetails 65. A dovetail is distinguished in that it is wider at its free end than at its interior end. As shown in FIG. 1a, all surfaces of dovetail sockets 70 extend perpendicular to the major surfaces of dovetail board 11. Pin board 15 includes wedge-shaped pins 80 extending from an end of pin board 15. Side surfaces 80s of pins 80 extend perpendicular to a base 81. Pin exterior sides 80b are narrower than pin interior sides 80a. Pins 80 are sized, shaped, and positioned to mate with dovetail sockets 70 when pins 80 are inserted into sockets 70. The wedge shape of pins 80 combined with the wider free ends of dovetails 65 prevents pins 80 from being extracted from dovetail board 11 except in a direction parallel to a major surface of pin board 15. The serpentine nature of dovetail joints also provides a large gluing surface. These characteristics make dovetail joints desirable for fine furniture and other application where durability and tight fit are desired.
Apparatus and a method for forming dovetail joints using templates and a router are described in U.S. Pat. No. 4,168,730. This patent was obtained Sep. 25, 1979 by the present inventor, and is incorporated herein by reference. This patent discloses forming dovetail joints using a router with templates and corresponding router bits which allow a user to form dovetail joints extremely accurately with minimum setup time. The tool set reduces the tendency for the router to tip relative to the template and/or work, and can be used by both amateur carpenters and precision woodworking craftsmen.
As shown in FIG. 2a, according to U.S. Pat. 4,168,730, two templates, dovetail template 12 and pin template 14 are provided. As shown in FIG. 2b, template 12 is attached by a screws 71 to a fence 66 against which a board 64 is placed and held for cutting. The board 64 may be held as shown by clamp 68, or by other clamping means such as toggle, cam, or air actuated clamps, clamping bars or cauls, or machine screws or bolts. Dovetail bit 16, turned by a router, not shown, is guided by bearing 36 against surfaces 24 of template 12 to make dovetail shaped socket cuts in dovetail board 64. Likewise, as shown in FIG. 2c, pin template 14 is attached to a fence 76, and a pin board 72 is clamped to fence 76 for cutting of pins using pin bit 18. Guide bearings 36 and 56 located at the neck of dovetail and pin bits 16 and 18 respectively, guide the router along the respective template.
U.S. Pat. 4,168,730 also shows a method for making dovetail joints using a pin board thicker than the length of the dovetail bit. As shown in FIG. 2d, in addition to removing waste from between the pins, a portion greater than the maximum thickness which the dovetail bit can reach is rabbeted away from the interior surface of the pin board. As shown in FIG. 2e, a correspondingly rabbeted fence 96 is used with fence 94 and pin template 14 such that pin board 90 can be supported against the rabbeted fence 96 while the pin cuts are being made. As shown in FIG. 2f, the width E of the rabbeted cut is made equal to the thickness of the dovetail stock.
Since U.S. Pat. No. 4,168,730 was applied for, further variations in the apparatus and method have been made. The "Owner's Manual", Keller Dovetail Templates, available from Keller & Co., 1327 I Street, Petaluma, CA 94952, copyright 1989, describes certain of these Variations. As shown in FIGS. 3a-3d, a set of dovetail and pin templates and router bits is provided, as before. However, pin template 314 includes open ends 342. Open ends 342 extend between guide surfaces such as 342a and 342b which are for shaping two sides of the same pin. With the ends open, it is possible to move a router so that bit 18 passes away from one slot in the pin board and into the next slot without the need for lifting the router away from the upper surface of pin template 314.
Additionally, as shown in FIGS. 4a-4c, scribed lines 418 and 419 are provided on lower surfaces of both templates 412 and 414 to assist the user in attaching fences 466 and 476 respectively. In the case of the dovetail template 412, there must be a distance B between a back surface 444 of each socket guide 443 and the working surface 468 of fence 466 for the center of the dovetail bit (not shown in FIG. 4a) to pass beyond the edge of the dovetail board This way the dovetail bit can cut the dovetail board clean through. If the distance B is somewhat larger than necessary, there is no change in the fit of the finished cuts, thus the position of template 412 against fence 466 is not critical. It is generally important, however, that template 412 be mounted to fence 466 such that edge 468 is perpendicular to openings 443. Aligning the fence 466 with scribe line 418 assures this perpendicularity, and further assures that fence 466 is parallel to the long edge of template 412.
In the case of pin template 414, as shown in FIG. 4b, it is essential for proper joint fit that fence 476 be properly positioned along pin template 4-4 such that distance C, which is the distance between the intersection 477a of one opening 473 with fence edge 478 and the intersection 477b of the next opening 474 with fence edge 478, be essentially the same as the diameter of the lower edge of the largest dovetail bit to be used. If the distance C is too small, the pins 80 which remain after waste is removed from pin board 15 will be too small, and the joint will be too loose. Conversely, if the distance C is too large, the joint will be too tight. In order to allow for fine adjustment, for example during initial setup of the template, or when the bit must be sharpened and becomes slightly smaller, screw holes 421 are formed as elongated slots so that the position of template 414 against fence 476 can be finely adjusted.